Add support for XCB surfaces via xcffib

[tych0]

Hi, I'm in the process of rewriting xpyb, so xcffib is unreleased but nearing a 0.1 release. I'd be happy to tag something if it means that you'd be more comfortable merging this :-)

[SimonSapin]

Thanks for contributing! I’d like to see a few things before merging this, though:

• Tests should pass (see https://travis-ci.org/SimonSapin/cairocffi/builds/27920322)
• There should be some tests for the new feature
• Some version of xcffib should be available on PyPI

[SimonSapin]

mkconstants.py is generally not run on the user’s system, it’s only used during development of cairocffi itself to generate constants.py. (I just moved it into utils/ to reflect this. You’ll have to adapt your PR, sorry.) Therefore, it should not have conditional code: whether xcffib is available when mkconstants.py runs is unrelated to whether it’s available when cairocffi is used.

It’s only at run-time that we should detect availability and fall back. I think cairocffi/pixbuf.py has a good way to do this.

Also, rather than having an entire class in a try … except block, I’d rather have a cairocffi.xcb module that requires xcffib (again, like cairocffi/pixbuf.py).

[flacjacket]

I have problems trying to run with this with the addition of CAIRO_STATUS_JBIG2_GLOBAL_MISSING, since I have cairo 1.12.16, while that isn't added [1] until 1.13. The error I get is:

bin/libqtile/__pycache__/_cffi__x25ffa352x2cba2200.c: In function ‘_cffi_e_enum__cairo_status’:
bin/libqtile/__pycache__/_cffi__x25ffa352x2cba2200.c:1879:8: error: ‘CAIRO_STATUS_JBIG2_GLOBAL_MISSING’ undeclared (first use in this function)
   if ((CAIRO_STATUS_JBIG2_GLOBAL_MISSING) < 0 || (unsigned long)(CAIRO_STATUS_JBIG2_GLOBAL_MISSING) != 38UL) {

[1] http://cgit.freedesktop.org/cairo/commit/?id=5c0caa6f82374ec38a33d5f25a725f60bc121887

[SimonSapin]

@flacjacket could you provide steps to reproduce this issue?

[flacjacket]

Well, I get that trying to run a WIP version of qtile using cairocffi and xcbffi. The file in question causing the problem is here https://github.com/tych0/qtile/blob/cffi/libqtile/pangocffi.py

[flacjacket]

Actually, I've worked out a more simple test case (tho it is not related to this PR, as doing this with travis, which has cairo 1.10.2, throws the same error but with many more undeclared values):

from cffi import FFI
import cairocffi

ffi = FFI()

ffi.include(cairocffi.ffi)

C = ffi.verify("""
    #include <xcb/xcbext.h>
    #include <cairo/cairo.h>
    #include <cairo/cairo-pdf.h>
    #include <cairo/cairo-ps.h>
    #include <cairo/cairo-svg.h>
""")

I don't know if this is a bug here, or a problem with using cffi, as the cairocffi docs has an example of doing simple pangocairo [1] and uses ffi.dlopen(...). While that works for that simple case, it doesn't allow additional cdef's to be verified.

[1] https://pythonhosted.org/cairocffi/cffi_api.html#example-using-pango-through-cffi-with-cairocffi

[SimonSapin]

@flacjacket, this is unrelated to this PR, please open a separate issue.

But, shortly: It is a very deliberate choice to use dlopen rather than verify in cairocffi so that users do not need to have a C compiler correctly configured to find cairo headers, which can be tricky especially on Windows. I don’t know if CFFI supports mixing dlopen and verify in the same FFI instance.

[tych0]

Going to close this in favor of #39.